IC chips come in a variety of forms such as dynamic random access memory (DRAM) chips, static random access memory (SRAM) chips, read only memory (ROM) chips, gate arrays, and so forth. The chips are interconnected in myriad combinations on printed circuit boards by a number of techniques, such as socketing and soldering. Interconnections among chips arrayed on printed circuit boards are typically made by conductive traces formed by photolithography and etching processes. Semiconductor circuit devices, including DRAMs, SRAMs and gate arrays are essentially switching devices.
One circuit-board-mounted semiconductor chip array that is of particular interest is the SIMM (single in line memory module). SIMM boards are typically constructed with such capacitors, which are usually located beneath or adjacent memory array circuit chips on the SIMM. Single in line packages (SIPs) are similar in design to SIMMs, except that instead of having a card edge-type connector, SIMMs have pins which are either socketably or solderably mounted on a bus. SIMMs are described in U.S. Pat. No. 4,727,513, to Clayton and assigned to Wang Labs, and in Micron Semiconductor's DRAM Data Book for 1993.
SIMM (single in line memory module) boards are circuit arrays which consist of byte multiples of memory chips arranged on a printed circuit board or comparable mounting arrangement. The SIMM board is connected to a circuit control board by an edge connector.
The SIMM is a highly space-efficient memory board having no on board address circuitry and which is designed to plug directly into the address, data and power-supply busses of a computer so that the randomly-addressable memory cells of the SIMM can be addressed directly by the computer's CPU rather than by a bank-switching technique commonly used in larger memory expansion boards. Memory cells on the SIMM are perceived by the computer's CPU as being no different than memory cells found on the computer's mother board. Since SIMMs are typically populated with byte multiples of DRAMs, for any eight bit byte or sixteen bit byte or word of information stored within a SIMM, each of the component bits will be found on a separate chip and will be individually addressable by column and row. One edge of a SIMM module is a card-edge connector, which plugs into a socket on the computer, is directly connected to the computer busses required for powering and addressing the memory on the SIMM.
SIMMs and related modules are constructed with JEDEC standardized terminal configurations, examples being JEDEC 72 pin configuration and JEDEC 30 pin configuration. At present, the 72 pin configuration has several "no connect" terminals. If a computer motherboard provides potential at one of the "no connect" terminals, a conventional module will not be affected.
For purposes of this disclosure, the reference to a "standard compatible module" means a module that is intended to be plug fit into a type of computer or other circuit board and which is in a format that is industry generic. Standard compatible modules are able to be installed onto the computer or other circuit board and meet expectations as to pin locations of power supply and other signal lines. Modules which meet JEDEC standard configurations would be standard compatible modules. At the time of the filing of this disclosure, there is not believed to be an industry standard for SIMM modules that accept nonstandard power supply potentials.
The control board may be any of a number of circuits which address memory arrays. Examples include computer mother boards, daughter boards which plug into a mother board, wherein the daughter board functions as a mother board for the SIMM module, peripheral devices with a capability of using add-on memory, and special purpose equipment which uses memory. It is also possible to use small modules of arrays of similar circuit for purposes other than memory applications.
A computer's power supply circuit must accommodate the demands and fluctuations of most or all internal devices in the computer, including the CPU and related circuitry, memory devices, and storage devices. In addition, the availability of corresponding "clean" power from line current is limited. The ability to accommodate tight tolerances of potentials for a portion of the computer may add undue complexity to the entire power supply circuit. When multiple circuits are connected to a single power supply, it is likely that the current draw of the multiple circuits will cause fluctuations in the power supply circuit. Therefore, it is advantageous to have a circuit for limiting variations in potential located on individual units, such as SIMM boards.
DRAM semiconductor memory parts are typically rated at a power supply potential V.sub.cc of 5.0 volts .+-.10%. Some manufactured parts are less than fully reliable when V.sub.cc varies by 10%, and so are rated at .+-.5%, or are otherwise subject to reduced tolerance to variations in potential.
A popular voltage regulator circuit is a three-pin device that can achieve a regulation of potential to a tolerance of approximately .+-.1%. This circuit generates a potential drop from its input to its output, so that the input power supply requirement for the voltage regulator circuit is that the power supply potential be approximately 1 volt higher than its output. This means that the use of such a voltage regulator circuit would reduce potential at its output to unacceptably low levels, or that potential at the supply be unacceptably high for operation without the voltage regulator circuit.
In the use of boards designed to function at reduced potentials, such as a daughter board having 3.5 volt devices that and connected to a 5 volt mother board, it is advantageous if reduced power boards have a circuit that allows the reduced power board to adapt to use with the higher voltage board.
It would likewise be desirable to provide modules with a power supply at a high potential and permit a voltage regulator circuit on the module to reduce the potential on the module to a desired level. This would provide a stable power output. It would be further desirable that a motherboard also be able to operate with modules that do not have the voltage regulator circuit.